It is well known that backing up a vehicle with a trailer attached is a difficult task for many drivers. This is particularly true for drivers who are untrained at backing with trailers such as, for example, those who drive with an attached trailer on an infrequent basis (e.g., have rented a trailer, use a personal trailer on an infrequent basis, etc). One reason for such difficulty is that backing a vehicle with an attached trailer requires counter-steering that is opposite to normal steering when backing the vehicle without a trailer attached and/or requires braking to stabilize the vehicle-trailer combination before a jack-knife condition occurs. Another reason for such difficulty is that small errors in steering while backing a vehicle with an attached trailer are amplified, thereby causing the trailer to depart from a desired path. Still another reason is that there are often objects and/or structures present that limit available space through which the trailer is to be backed.
To assist the driver in steering a vehicle with trailer attached, a trailer back-up assist system needs to know the driver's intention. One common assumption with known trailer back-up assist systems is that a driver of a vehicle with an attached trailer wants to back up straight and the system either implicitly or explicitly assumes a zero curvature path for the vehicle-trailer combination. Unfortunately, most of real-world use cases of backing a trailer involve a curved path and, thus, assuming a path of zero curvature would significantly limit usefulness of the system. Some known systems assume that a path is known from a map or path planner. To this end, some known trailer back-up assist systems operate under a requirement that a trailer back-up path is known before backing of the trailer commences such as, for example, from a map or a path planning algorithm. Undesirably, such implementations of the trailer back-up assist systems are known to have a relatively complex Human Machine Interface (HMI) to specify the path, obstacles and/or goal of the back-up maneuver. Furthermore, such systems also require some way to determine how well the desired path is being followed and to know when the desired goal, or stopping point and orientation, has been met, using approaches such as cameras, inertial navigation, or high precision GPS. These requirements lead to a relatively complex and costly system.
As previously mentioned, one reason backing a trailer can prove to be difficult is the need to control the vehicle in a manner that limits the potential for a jack-knife condition to occur. A trailer has attained a jack-knife condition when a hitch angle cannot be reduced (i.e., made less acute) by application of a maximum steering input for the vehicle such as, for example, by moving steered front wheels of the vehicle to a maximum steered angle at a maximum rate of steering angle change. In the case of the jack-knife angle being achieved, the vehicle must be pulled forward to relieve the hitch angle in order to eliminate the jack-knife condition and, thus, allow the hitch angle to be controlled via manipulation of the steered wheels of the vehicle. However, in addition to the jack-knife condition creating the inconvenient situation where the vehicle must be pulled forward, it can also lead to damage to the vehicle and/or trailer if certain operating conditions of the vehicle relating to its speed, engine torque, acceleration, and the like are not detected and counteracted. For example, if the vehicle is travelling at a suitably high speed and/or subjected to a suitably high longitudinal acceleration when the jack-knife condition is achieved, the relative movement of the vehicle with respect to the trailer can lead to contact between the vehicle and trailer thereby damaging the trailer and/or the vehicle.
As also previously mentioned, another reason backing a trailer can prove to be difficult is that there are often objects and/or structures present that limit available space through which the trailer is to be backed. A driver must therefore be concerned with not only backing the trailer to an intended location but also with doing so in a manner whereby neither the vehicle nor the trailer collide with adjacent objects and/or structures. Contributing to this challenge is that the potential for the vehicle and trailer to attain a jack-knife condition limits maneuverability for navigating through such object without hitting them.
Therefore, a solution for providing trailer back-up assist with object avoidance would be beneficial, desirable and useful.